A number of performance specifications have been established for diesel fuels of different grades depending upon service application. A number of different properties are set out in these specifications including, for example, flash point, cloud point, pour point, viscosity, sulfur content, distillation range, gravity and ignition quality. Of these, the ignition quality is an important parameter and is usually expressed in cetane number (CN) determined by the standard ASTM test method D613. Diesel fuels of high cetane number differ from those of lower cetane numbers by having shorter ignition lags when the fuel is injected into the cylinders of the engine. Fuels of high-cetane number also ignite at lower compressed air temperatures than the lower-cetane fuels, permitting the engine to be started at lower temperatures and to be brought to a steady running condition more quickly with less combustion knock.
Viscosity is another important characteristic of diesel fuels, affecting leakage in the fuel pump and the power required to operate the pump as well as having an influence on the size of the fuel droplets sprayed into the cylinder through the injection nozzles. Viscosity is typically expressed as kinematic viscosity, determined by ASTM test D445.
Current environmental regulations are setting stricter specifications on diesel fuels, especially in terms of sulfur content and aromatics level. Sulfur is, of course, associated with the production of acidic oxides of sulfur, a troublesome atmospheric pollutant. Aromatics are considered undesirable not only for their adverse effect on ignition quality but also because they have been implicated with the production of significant amounts of particulates in the engine exhaust.
One type of service where increasing government regulation is being proposed is in underground mines where a concern for improved air quality standards has been expressed. Although improved engine design and maintenance, increased air circulation or a reduced level of engine operations in the mines could improve air quality, each of these presents its own problems. Another solution lies in the use of fuels which result in lower levels of harmful emissions.
The present invention provides a diesel fuel which produces low levels of engine emissions and which can be readily produced in existing refineries by proper observance of product specifications coupled with suitable additive use. The present diesel fuel compositions are especially suitable for use in underground diesel-engined mining equipment and are capable of reducing all of the currently regulated emissions subject to government regulation, namely, carbon monoxide, oxides of nitrogen, unburned hydrocarbons and particulates. The properties of the present low emission fuels are low sulfur content, low final boiling range and a high but controlled emission quality.